H-dibaryon and hypernucleus formation in the Ξ-12C reaction at rest -: art. no. 055201

Stopped-Xi-C-12 reactions have been investigated with respect to H-dibaryon and hypernucleus formation with a scintillating fiber detector. Out of 5.5x10(3) tagged Xi (-) particles via the (K-,K+) reaction we obtained 72 stopping Xi (-) events with 6.7(-1.4)(+1.1) background events after imposing kinematic constraints. Hypernuclear production has been studied by observing free Lambda decays in the stopped-Xi (-) reactions. From the observed Lambda momentum spectrum, we have found the hypernuclear production rates to he 18+/-13, 65+/-6, and 17+/-12 % for double/twin-Lambda hypernucleus, single-Lambda hypernucleus, and no hypernucleus cases, respectively. With the same sample, we set upper limits on R (stopped-Xi C-12-->HX/stopped-Xi (-) C-12--> all) for H decaying into Lambdan, Sigma (-) p, and Lambdap pi (-), for H masses just below Lambda Lambda mass threshold and for H lifetime range 10(-11) less than or equal to tau (H) less than or equal to 10(-8) s. The upper limits on R are similar to0.1-0.2, assuming all of the H decay into each decay mode. Our results give a tight constraint on the existence of the bound H, in comparison with the theoretical estimates of Aerts and Dover, albeit with different target nuclei.